Communication And Homeostasis Basics

Question 1

How does animals responding to their environment help the organism to survive?

Answer 1

-respond to changes in their external environment e.g by avoiding harmful environments such as places that are too hot or too cold
-respond to changes in their internal environment to make sure that the conditions are always optimal for their metabolism

Question 2

What is a stimulus

Answer 2

Any change in the internal or external environment

Question 3

Explain the process of how a response is created within the body

Answer 3

1) receptors detect stimuli
2) receptors are specific, they only detect one particular stimulus e.g light or pressure
3) there are many types of receptor that each detect a different type of stimulus
4) some receptors are cells e.g photoreceptors are receptor cells that connect to the nervous system. Some receptors are proteins on cell surface membranes
5) effectors are cells that bring about a response to a stimulus, to produce an effect. They include muscle cells and cells found in glands e.g the pancreas

Question 4

What is cell signalling?

Answer 4

-the communication between cells
-only complementary messenger molecules will trigger a response in a target cell
-it can occur between adjacent cells or between distant cells
-cell surface receptors allow cells to recognise the chemicals involved in cell signalling

Question 5

Explain how the nervous communication system works

Answer 5

-an interconnected network of neurones that send electrical signals connected by synapses
-neurotransmitters are released by nerve endings at synapses and neuromuscular junctions
-the transmitters diffuses across the gap and binds with the receptors on the post-synaptic membrane
-as a result nerve impulses are generated at a synapse or muscles contracts at a neuromuscular junction
-it is an extremely fast response
E.g flight or flight

Question 6

Explain how the hormonal communication system works

Answer 6

-hormones are chemical messengers made by endocrine glands
-they are released from the gland directly into the blood stream which transports them to their target cells
-the hormones diffuse from the blood to the target cells and either bind with receptors or pass through the membrane
-can be a fast or slow response, but works longer term
E.g growth

Question 7

What are internal factors?

Answer 7

-kept constant by epithelial tissues and organs (e.g animals skin, plants bark)
-in animals, tissue fluid forms the internal environment around cells. Cells also produce waste products such as carbon dioxide which can act as a stimulus for other cell mechanisms to excrete waste

Question 8

What are external factors?

Answer 8

-factors that change in the external environment e.g temperature, pH, chemicals, light
-this may be a gradual response e.g response to seasons arctic fox coat colour change

Question 9

Explain why temperature needs to be maintained inside of mammals

Answer 9

-temperature affects all metabolic reactions
-low temperatures can slow down metabolic rate
-high temperatures can disrupt membranes (making them leaky), and damage proteins including enzymes (denature) slowing or stopping metabolic rate

Question 10

What are the symptoms of hypothermia?

Answer 10

-shivering
-pale, cold and dry skin
-slurred speech
-slow breathing
-tiredness or confusion

Question 11

What are the symptoms of hyperthermia?

Answer 11

-blurred vision
-dizziness
-fast breathing
-fatigue
-headache
-light headedness
-low blood pressure
-muscles ache or cramp

Question 12

Explain why water/salt balance needs to be maintained inside of mammals

Answer 12

-changes in the water and salt content of the blood affects it’s water potential
-changed water potential could result in movement of water into cells (causing lysis) or movement of water out of the cells (slowing their metabolism)
-high salt content also increases retention of water, so increasing blood volume and blood pressure

Question 13

Explain why blood glucose needs to be maintained inside of mammals

Answer 13

-glucose is a major fuel for respiration
-it is the only fuel for some cells e.g brain cells
-if glucose is low it can slow respiration rate
-if glucose is high it affects the water potential causing water to leave cells, glucose may be excreted in urine

Question 14

Explain why blood pressure needs to be maintained inside of mammals

Answer 14

-blood pressure is determined by the force of contraction of the heart muscle and the diameter of the blood vessels
-if blood pressure becomes too high it may damage delicate blood vessels and cause their rupture
-if blood pressure becomes too low your organs don’t get enough oxygen or nutrients

Question 15

Explain why carbon dioxide needs to be maintained inside of mammals

Answer 15

-co2 is a waste product from aerobic respiration
-it is an acid gas and can lower the pH of blood which can affect the 3D shape of proteins and their functioning

Question 16

What makes a good communication system?

Answer 16

1) it will cover the entire body
2) it will enable cells to communicate with each other
3) it will enable specific communication
4) it will enable a rapid communication system
5) it will enable both short term and long term responses

Question 17

What is homeostasis?

Answer 17

-involves control systems that keep your internal environment roughly constant
-keeping your internal environment constant is vital for cells to function normally and to stop them being damaged

Question 18

What is meant by negative feedback mechanism?

Answer 18

-enables the body to maintain a stable state
-very common in the body
-once the conditions are back to normal a message is sent back to the control centre to turn off the actions

Question 19

What is meant by positive feedback mechanisms?

Answer 19

-some changes trigger a positive feedback mechanism which amplifies the change
-the effectors respond to further increase the level away from the normal level
-it is useful to rapidly activate something
e.g a blood clot after an injury- platelets become activated and release a chemical, triggering more platelets to be activated and so on. They very quickly form a blood clot at the injury site. The process ends with negative feedback, when the body detects the blood clot has been formed
-positive feedback isn’t involved in homeostasis because it doesn’t keep your internal environment constant

Question 20

What is an ectotherm? Give an example

Answer 20

-animals that rely on ‘outside sources of heat’ to maintain their body temperature
-they can’t control their body temperature internally
-they control temperature by changing their behaviour
-e.g the namaqua chameleon (reptiles and fish)

Question 21

Explain how the namaqua chameleon maintains its body temperature through behavioural adaptations

Answer 21

-black in the morning but pale grey underneath = absorb as much as sun and heat as possible
-it orientates it’s body towards the sun = create a larger surface area so can absorb maximum amount of sunlight
-during the day it turns a very pale grey colour = to reflect as much as heat to cool off
-opens its mouth and pants in the middle of the day = to cool off by evaporation of water from surfaces and radiation from tissues

Question 22

What is an endotherm?

Answer 22

-an organism that regulates its body temperature internally through homeostasis
-they can also control their temperature by behaviour e.g by finding shade
-e.g mammals and birds

Question 23

In an endotherm what detects a change in surface temperature of skin and a change in internal body temperature

Answer 23

-surface temperature of skin = peripheral temperature receptors
-internal body temperature = hypothalamus

Question 24

Explain how the hypothalamus works in controlling internal body temperature

Answer 24

-acts as a coordinator for some homeostatic mechanisms
-it receives information about temperature from thermoreceptors, and thermoreceptors in the skin (peripheral temperature receptors) detect external temperature
-thermoreceptors send impulses along sensory neurones to the hypothalamus which sends impulses along motor neurones to effectors e.g skeletal muscles or sweat glands
-has 2 sections for temperature regulation
-heat gain centre is activated by a drop in temperature
-heat loss centre is activated by a rise in temperature
-these centres gain information from thermoreceptors

Question 25

What are the cooling mechanisms that endotherms use to decrease body temperature?

Answer 25

-vasodilation= arteriole muscles relax causing the arterioles near the skin to dilate and allowing more blood flow through skin capillaries. This means heat is lost from the surface to the environment through radiation

-sweating = sweat is secreted by sweat glands. This cools the skin by evaporation which uses heat energy from the body to convert liquid water into water vapour

-flattening of hairs = the hair erector muscles in the skin relax, causing hairs to lie flat. This stops them from forming an insulating layer by trapping air and allows air to circulate over skin and heat to leave by radiation

Question 26

What are the warming mechanisms that endotherms use to increase body temperature?

Answer 26

-vasoconstriction= arteriole muscles constrict which restricts the amount of blood flow to the capillaries. Instead the blood is diverted through shunt vessels which are further down in the skin, therefore do not lose heat to the environment. This minimises the loss of heat to the environment via radiation

-boosting metabolic rate= most of the metabolic reactions in the body are exothermic and this provides warmth to the body. In cold environments the hormone thyroxine increases the basal metabolic rate increasing heat production in the body

-shivering = this is a reflex reaction in response to a decrease in core body temperature. Muscles are the effectors and they contract in a rapid and regular manner. The metabolic reactions required to power this shivering generate sufficient heat to warm the blood and raise the core body temperature

-erection of hairs = the hair erector muscles in the skin contract, causing hairs to stand on end. This forms an insulating layer over the skins surface by trapping air between the hairs and stops heat from being lost by radiation

Question 27

Describe the sequence of events resulting from a decrease in body temperature

Answer 27

1) decrease in temperature is detected by thermorecpetors
2) impulses are sent via sensory neurones to the hypothalamus
3) vasoconstriction occurs, hairs stand up on their ends, increased metabolic rate, shivering
4) core temperature increases back to normal
5) receptors detect change and turn negative feedback system off